1. Field of the Invention
The present invention relates to photosensitive and/or thermosensitive chromogenic compositions, recording or reproduction materials utilizing these sensitive compositions and processes for producing colored images utilizing these materials. More particularly, the present invention relates to compositions for producing colored images wherein the reaction between a sensitive chromogenic compound (including the dissociation or decomposition or isomerization product of the sensitive chromogenic compound) with a phenolic coupler compound is responsible for the formation of colored images.
2. Discussion of the Prior Art
The use of photosensitive compounds and compositions and thermosensitive compounds and compositions that change color or intensity or form color reactive compounds when exposed to light and/or heat, have long been used in light sensitive and heat sensitive compositions used in forming colored images and reproductions. For example, on exposure to light of certain wavelengths, photochromic compounds undergo a reversible color change; i.e., they become colored under the influence of light of certain wavelengths, whereas upon irradiation with other, usually longer wavelengths, they exhibit a tendency to revert to the colorless state. While the reversibility of the color change of photochromic and thermochromic compounds and compositions have been taken advantage of in various processes, such as photography or photolithography, the reversibility of the color change has prevented the use of such substances in compositions and processes wherein it is desired to produce a permanent image. Accordingly, the prior art has developed several approaches to provide permanent colored images utilizing photochromic and thermochromic compounds. One commonly accepted and often successful approach has been to provide compositions wherein a photosensitive or thermosensitive chromogenic compound is caused to undergo an irreversible chemical reaction to form a permanent colored image subsequent to exposure to light and/or heat.
Particularly useful chromogenic compounds and compositions which have been used in this type of system include those chromogenic compounds which are capable of reacting with a phenolic compound to produce a permanent colored image.
One class of chromogenic compounds which has been found to be particularly useful in its ability to form permanent colored images by combining with a phenolic compound is the class of spiropyran compounds. For example, Baum, in U.S. Pat. No. 3,451,338, describes a thermographic method of data-recording and heat-sensitive record sheets which include chromogenic indolinospirobenzopyran compounds and di-phenol material which produce immediate and lasting color when and where the two co-reactant materials are brought into liquid contact. Generally, the liquid environment is the result of the application of heat which results in the melting of one or both of the co-reactant materials or a polymeric film binder.
The chromogenic properties of triphenylmethane derivatives are also well known and have been utilized in various sensitive compositions and recording materials. For instance, Baum, in U.S. Pat. No. 3,539,375, describes a modification of his earlier thermographic recording system wherein the chromogenic material is crystal violet lactone where the lactone and phenolic reactant are dispersed in a matrix of polyvinyl alcohol. Similar heat sensitive record materials have been described in Blose, et al., U.S. Pat. No. 3,674,535 and French Patent No. 2,172,386.
Various ferric salts, especially ferric salts of organic acids, such as those disclosed in U.S. Pat. No. 2,663,654, to Miller, et al. have also been known as chromogenic compounds which form colored images upon reaction with phenolic compounds.
One of the oldest recording systems utilizing the reaction between phenolic compounds and photosensitive compounds for producing color reactions is in the field of diazo-reproduction. Diazo processes have been long used for reproducing blueprints and in reproduction of high-resolution microfilm. The basic diazo process used in blueprint reproduction processes as well as in microfilm reproduction processes includes dissociation of a diazonium salt by irradiation with ultraviolet light followed by the reaction of the unirradiated salts with phenolic or amine-type reactants so as to produce an azo dye capable of forming contrast in the image reproduction. The reaction between the diazonium salt and phenolic or amine-type reactants is referred to as a coupling reaction. In the present specification, the term "coupling reaction" will be used to refer to any reaction between a phenolic "coupling" compound and a chromogenic compound which yields a colored reaction product. French Patent No. 1,336,307 provides one example of a coupling reaction utilizing recording materials containing diazonium compounds which react with free phenolic compounds to create colored images.
However, the development of these processes utilizing the reaction between a phenolic compound and a photosensitive or thermosensitive chromogenic compound have met with various drawbacks which have limited their widespread usage. For instance, the phenolic compounds are readily oxidized by air giving colored quinone compounds which tend to produce a disagreeable background color. There has also been a tendency for premature color reactions between the phenolic compounds and the chromogenic compounds. These drawbacks have resulted in unsatisfactory shelf lives for the sensitive recording materials utilizing these sensitive compositions. In addition, the colored images have not yet proven to be permanently irreversible in many instances.
As one attempt to solve this deficiency, it has been known to encapsulate the co-reactant materials. However, such technique, itself, presents difficult procedures in the formation of the encapsulated product and the resulting products are often fragile and limited in storage life. Moreover, various of the techniques which have been utilized to stabilize the phenolic coupling compounds in order to prevent them from reacting prematurely or causing disagreeable heightening of the background of the sensitive recording material have not proved successful since they resulted in undesirable lowering of the reaction speed during the actual recording process.